An electrophotographic image forming apparatus including a photoconductor is known. In this apparatus, an electrostatic latent image is formed on a surface of a charged photoconductor, the latent image is developed into a developer image by developer, and the developer image is transferred onto a recording medium to form an image on the medium. After the developer image is transferred onto the recording medium, a discharger eliminates remaining charge from the surface of the photoconductor as preparation for next image formation.
Patent Document 1 discloses a photoelectric discharger as an example of the discharger. The photoelectric discharger includes an optical fiber extending in a direction of a central axis of the photoconductor to face an outer peripheral surface of a photoconductive drum, and a lamp, i.e. a light source, disposed alongside the photoconductive drum in the central axis direction.
The optical fiber has a core, i.e. a bar-like transparent glass, a clad, i.e. a cylindrical transparent glass or the like covering the core, and a reflecting tape attached to the outer periphery of the clad. The outer peripheral surface of the core has a diffusion surface formed as a consequence of fine irregularity processing.
The photoelectric discharger operates as follows: Light emitted from the lamp enters the optical fiber, and is reflected by the reflecting tape toward the diffusion surface. The light is diffused by the diffusion surface to enter the core, and then irradiated onto the outer peripheral surface of the photoconductive drum while being reflected by the boundary between the core and the clad. Accordingly, the outer peripheral surface of the photoconductive drum is exposed, and charges remaining on the outer peripheral surface of the photoconductive drum are eliminated therefrom.
Patent Document 1: Japanese Published Unexamined Patent Application No. S62-127786
The photoelectric discharger disclosed in Patent Document 1 is complicated in configuration because the number of components (core, clad, and reflecting tape, etc.) of the optical fiber is large and the diffusion surface must be formed on the core by applying irregularity processing.
The optical fiber also suffers from a problem in that light emitted from the lamp hardly reaches a position distant from the lamp in the central axis direction of the photoconductive drum. Therefore, the light irradiation amount onto the outer peripheral surface of the photoconductive drum from the optical fiber at this distant position is smaller than the irradiation amount at a position close to the lamp. In this case, it is difficult to eliminate charges uniformly across the central axis direction from the outer peripheral surface of the photoconductive drum. Accordingly, when charging the photoconductive drum for next image formation, the outer peripheral surface of the photoconductive drum is hardly charged uniformly across the central axis direction, and this causes fluctuation in density of the developer image transferred on the recording medium in the central axis direction of the photoconductive drum, and satisfactory image formation may not be realized.